This invention relates to a method of inhibiting the growth of Nitrosomonas, a method of suppressing the nitrification of ammonium nitrogen in soil and compositions useful for these purposes.
Since most plants obtain the greater part or all of their nitrogen requirements from the soil, it is one of the most important agricultural problems to provide nutrient nitrogen for the growth of plants in soil. Available nitrogen in soil is present in the three forms of organic nitrogen, ammonium nitrogen and nitrate nitrogen. Among them, ammonium nitrogen and nitrate nitrogen are well absorbed from soil and utilized by plants. Organic nitrogen, which may originate from manure, crop residues and organic fertilizers, is typically converted by soil bacteria to ammonia or ammonium salts, in which form it becomes available to the plant.
In agricultural practice, ammonium nitrogen is frequently provided either directly as anhydrous ammonia or ammonium salts, or indirectly as organic fertilizers such as urea which release ammonia in the soil. A valuable characteristic of ammonium nitrogen is that it reversibly binds to soil particles by cation exchange. In this form it resists leaching from the soil, yet remains readily available to plant roots. However, widespread soil bacteria of the genus Nitrosomonas oxidize ammonia to nitrite ion which later undergoes both spontaneous and microbial oxidation to nitrate. This process, termed nitrification, does not immediately decrease available soil nitrogen but does lead to several undesirable consequences. Nitrite and nitrate, being anions, no longer bind to soil and are rapidly leached beyond reach of the crop root system. In addition, they are degraded by a variety of soil microbes to free nitrogen and nitrogen oxides. The resulting loss of fertilizer nitrogen may amount to as much as forty percent of that applied, and is reflected in lower crop yields. Other indirect consequences include contamination of streams and aquifers by the leached nitrite and nitrate ions and pollution of air by their nitrogen oxide products.
In order to prevent the loss of nitrogen from soil and to improve the rate of utilization of nitrogen by plants, it is necessary to suppress the nitrification of ammonium nitrogen by soil bacteria. One way to accomplish this is to inhibit the growth of the nitrifying soil bacteria Nitrosomonas spp.
At least two products are presently available commercially for the purpose of inhibiting soil nitrification. These products are etridiazol, marketed by Olin Mathieson Chemical Corporation under the trademark "Dwell", and nitrapyrin, marketed by the Dow Chemical Company under the trademark "N-Serve." There is a constant need for nitrification inhibitors which are more effective and/or more economical than those currently available.